Various known flame detectors evaluate optical signals of various wavelengths to determine the presence of fire. In general, this requires the use of special sensors and optical filters in order to distinguish fire from non-fire optical sources.
For example, multi-sensor detectors are disclosed in U.S. Pat. No. 4,370,557 entitled, “Dual Detector Flame Sensor,” which issued Jan. 25, 1983, U.S. Publication No. 2013/0068933 entitled, “Flame Detector Using Optical Sensing,” published Mar. 21, 2013, both of which are assigned to the Assignee hereof and incorporated herein by reference. U.S. Publication No. 2003/0178568, which published Sep. 25, 2003, discloses yet another form of multi sensor flame detector.
Some of the known detectors incorporate costly lead-salt quantum sensors, thermopiles, and pyroelectric sensors. Others use specialized narrowband thin-film optical interference filters. Further, some of the known detectors are limited to sensing only burning hydrocarbons.